1. Field of the Invention
The present,invention relates to a novel latent heat storage material composition suitable for use in air conditioning systems.
2. Description of the Prior Art
Heretofore, latent heat storage materials used in air conditioning systems which have melting points in the range of 5.degree. to 10.degree. C. have been considered useful. Examples of the known conventional organic compounds having melting points of around 5.degree. to 10.degree. C. include tetradecane (C.sub.14 H.sub.30, melting point: 5.degree. C.; Japanese Patent Publication No. 53-24182) and pentadecane (C.sub.15 H.sub.32, melting point: 9.9.degree. C.), etc., which are paraffinic compounds, and polyethyleneglycol #400 (melting point: 4.degree. to 8.degree. C.; Japanese Patent Application Laid-open No. 62-19968) and 1-decanol (melting point: 5.degree. C.), etc., which are non-paraffinic compounds. However, these compounds are scarcely used now, as they have low thermal conductivity and a relatively low heat of melting.
On the other hand, several compositions of inorganic compounds have been reported which are composed of inorganic salt hydrates having large heat of melting and melting points of around 5.degree. to 10.degree. C. For example, a binary composition composed of disodium hydrogenphosphate dodecahydrate and dipotassium hydrogenphosphate hexahydrate (melting point: 5.degree. C.; Japanese Patent Publication No. 52-11061) which has outstanding problems in the prevention of supercooling and, which therefore, has faced difficulties in practical use. A ternary composition composed of sodium sulfate decahydrate, ammonium chloride and ammonium bromide (Japanese Patent Publication No. 62-56912), which although it possesses a melting point of within the range of 6.3.degree. to 10.1.degree. C., is also not suitable for practical use because of its insufficient stability in long-term performance.
Another ternary composition composed of sodium sulfate decahydrate, ammonium chloride and sodium chloride is illustrated in Maria Telkes, SOLAR ENERGY STORAGE (ASHRAE JOURNAL, SEPTEMBER, 1974), but this composition has been known to have a melting point of 12.8.degree. C. In addition, a ternary composition composed of sodium sulphate, water and ammonium chloride (Japanese Patent Application Laid-open No. 2-92988) has a melting point of within the range of 8.6.degree. to 9.6.degree. C.
The preferable melting point of latent heat storage materials used for air conditioning systems has been considered to be from 5.degree. to 10.degree. C., and more preferably from 5.degree. to 8.degree. C. However, when already installed air conditioning systems are used with insufficient cooling, a conventional water heat-pump (e.g. an absorption refrigerator) must also be used simultaneously. In this case, the possibility that the temperature of the obtained cooled water would be restricted to about 4.degree. to 5.degree. C. is great. The latent heat storage materials which are to be frozen by the cooled water of 4.degree. to 5.degree. C. should have freezing points of 7.degree. to 8.degree. C., and, from the view point that it is preferable to have a melting temperature which is as low as possible, the melting point of the latent heat storage materials should optimally be in the range of 10.degree. to 13.degree. C.
On the other hand, for newly-installed air conditioning systems, it would be ideal for the refrigerator not to be operated in the daytime, but rather for the cooling to be performed by using only the latent heat stored at night.
Many latent heat storage materials having melting points of 5.degree. to 10.degree. C. proposed heretofore are not used in practice due to any one of the following reasons of (1) small amounts of heat storage, (2) a large difference between a starting temperature of crystallization and a freezing point, (3) no heat recycling stability in long-term performance, (4) high costs, etc.
Accordingly, the object of the present invention is to provide a latent heat storage material composition suitable for use in air conditioning systems and satisfying conditions such as (1) having a melting point in the range of 5.degree. to 10.degree. C., (2) having a large amount of latent heat at the melting point, (3) exhibiting heat recycling stability in long-term performance and (4) possessing the capability for heat storage by water (freezing by cooled water of 1.degree. to 2.degree. C.).